Method for producing compressor housing

ABSTRACT

A compressor housing is constructed by assembling a scroll piece and a shroud piece. The scroll piece includes an inlet cylindrical portion, a front side wall section, and an outlet cylindrical portion in which the inner wall surface of the outlet communicating section is curved to connect an inner wall surface of a scroll chamber and that of an outlet port. Fabrication of the scroll piece includes a die casting step that uses a back mold having a first projecting portion and a front mold having a second projecting portion projecting toward the back side to form an intermediate formed body wherein both the first and second projecting portions are disposed within the outlet cylindrical portion, and a cutting and removal step that removes residue portions in the intermediate formed body by cutting.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119 to Japanese Application No. 2015-232228, filed on Nov. 27, 2015, entitled “METHOD FOR PRODUCING COMPRESSOR HOUSING.” The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for producing a compressor housing for a turbocharger.

Description of the Related Art

Turbochargers, which are mounted in an automobile for example, are configured to compress intake air in the compressor and discharge the compressed air to the internal-combustion engine. Specifically, a scroll chamber into which the compressed air discharged from the impeller flows is provided on the air flow path formed within the compressor housing, the scroll chamber guides the compressed air to an outlet port, and the compressed air is discharged to the internal-combustion engine side through the outlet port.

The shape of the scroll chamber in particular greatly affects the performance of the compressor, and therefore it is necessary to form the shape suitably so as to conform to the performance requirements. In this regard, forming a compressor housing by gravity casting or low pressure casting may be conceived. These methods can implement casting using the so-called core and therefore provides enhanced geometric flexibility to be able to address complex shapes. However, the casting cycle lasts a long time and therefore the productivity is low, and since the core or another part is necessary, the cost is high. In addition, when a sand mold is used for example, there is another problem in that the surface roughness increases and therefore the efficiency of the compressor decreases.

On the other hand, die casting is also known as a method for forming a compressor housing. In die casting, the casting cycle is shorter than in gravity casting or low pressure casting and therefore the productivity is higher and the cost is lower. However, die casting can form only such shapes that can be pulled from the mold (i.e. shapes not including an undercut), and therefore has low geometric flexibility and cannot address complex shapes. In view of this, as disclosed in JP-A-2014-62492, there has been proposed a compressor housing constructed by assembling a scroll piece and a shroud piece, each formed as a discrete part, to each other. This is intended to ensure the geometric flexibility of the scroll chamber of the compressor housing while allowing each piece to be of a shape that can be easily formed by die casting.

PATENT DOCUMENTS Patent Document 1: JP-A-2014-62492

However, in the compressor housing disclosed in JP-A-2014-62492, the outlet port is provided so as to extend from the scroll chamber in the direction tangential to the circumferential direction. Thus, to form the scroll piece by die casting, it is necessary to use a core or it is necessary to prepare a die casting mold for forming the scroll chamber and a die casting mold for forming the outlet port separately and to withdraw the two die casting molds in different directions when the molds are withdrawn. Therefore, there are problems in that the mold structure is complex and the production process is complex and thus the production cost increases.

In addition, the shape of the outlet port affects the performance of the compressor and also affects its mountability to the vehicle engine room. Thus, it is not desirable to place priority only on ease of coring out when designing the shape of the compressor housing.

The present invention has been made in view of the foregoing problems and is intended to provide a method for producing a readily producible compressor housing for a turbocharger.

SUMMARY OF THE INVENTION

One aspect of the present invention is a method for producing a compressor housing for a turbocharger, the compressor housing being able to house an impeller,

the compressor housing including: an inlet port formed adjacent to a front side of the impeller, the inlet port opening to a front side in an axial direction; a scroll chamber formed on an outer circumferential side of the impeller in a circumferential direction; an outlet port on an outer circumferential side of the inlet port, the outlet port opening to the front side in the axial direction; and an outlet communicating section communicating between the outlet port and the scroll chamber,

the compressor housing being constructed by assembling a scroll piece and a shroud piece, each formed as a discrete part, together in the axial direction,

the scroll piece including: an inlet cylindrical portion making the inlet port and having a through hole in the axial direction; a front side wall section on an outer circumferential side of the inlet cylindrical portion, the front side wall section making a front area of a wall surface of the scroll chamber; and an outlet cylindrical portion extending from a region in a circumferential direction of the front side wall section, the outlet cylindrical portion making the outlet communicating section and the outlet port,

the outlet cylindrical portion being configured such that an inner wall surface of the outlet communicating section is curved so as to smoothly connect between an inner wall surface of the scroll chamber and an inner wall surface of the outlet port,

the shroud piece including: a shroud press-fit portion in a cylindrical shape to be press-fitted into the inlet cylindrical portion; an inner circumferential wall section making an inner circumferential area of the wall surface of the scroll chamber; a shroud surface opposed to the impeller; and a diffuser surface extending from the shroud surface toward the scroll chamber,

the method including: a die casting step forming an intermediate formed body by die casting, the intermediate formed body having a residue portion including a metal material left within the outlet cylindrical portion, the die casting using a back mold having a first projecting portion projecting toward the front side and a front mold having a second projecting portion projecting toward a back side, the front mold being movable back and forth relative to the back mold in the axial direction; and

a cutting and removal step removing the residue portion in the intermediate formed body by cutting so as to obtain the scroll piece, wherein, in the die casting step, both the first projecting portion and the second projecting portion are disposed within the outlet cylindrical portion.

The method for producing a compressor housing includes the die casting step and the cutting and removal step. In the die casting step, die casting is performed using the back mold and the front mold that are movable back and forth relative to each other in the axial direction. Furthermore, the die casting is performed in such a manner that the first projecting portion of the back mold and the second projecting portion of the front mold are positioned within the outlet cylindrical portion. This makes it possible to form, by die casting, an intermediate formed body having a shape close to the final shape of the scroll piece without using a core or the like.

Then, the residue portion in the intermediate formed body is removed by cutting in the cutting and removal step, and thereby the scroll piece can be readily produced. By performing the simple die casting step and the simple cutting and removal step in this manner, it is possible to readily produce the scroll piece. Consequently, production of the compressor housing can be readily accomplished and therefore the production man-hours and the production cost can be minimized.

As described in the foregoing, with the above aspect, it is possible to provide a method for producing a readily producible compressor housing for a turbocharger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view, as viewed from the front side, of a compressor housing according to Embodiment 1 with a seal plate assembled thereto;

FIG. 2 is a cross-sectional view, taken along a line III-III in FIG. 1 illustrating the compressor housing according to Embodiment 1 with an impeller mounted therein;

FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 1;

FIG. 4 is a cross-sectional view taken along a line IV-IV in FIG. 1;

FIG. 5 is a cross-sectional view taken along a line V-V in FIG. 1;

FIG. 6 presents perspective views of a scroll piece, shroud piece, and seal plate according to Embodiment 1;

FIG. 7 is a cross-sectional illustration depicting a die casting step according to Embodiment 1;

FIG. 8 is a cross-sectional illustration, taken along a line VIII-VIII in FIG. 7 depicting a first projecting portion, second projecting portion, and outlet cylindrical portion according to Embodiment 1;

FIG. 9 is another cross-sectional illustration depicting the die casting step according to Embodiment 1;

FIG. 10 is a cross-sectional illustration depicting a state after coring out in the die casting step according to Embodiment 1;

FIG. 11 is a cross-sectional view of an intermediate formed body according to Embodiment 1;

FIG. 12 is a perspective view of the intermediate formed body according to Embodiment 1;

FIG. 13 is a perspective view of the scroll piece according to Embodiment 1;

FIG. 14 is a cross-sectional view of the scroll piece according to Embodiment 1;

FIG. 15 is a plan view of the scroll piece according to Embodiment 1 as viewed from the back side;

FIG. 16 is a cross-sectional view of the compressor housing according to Embodiment 1;

FIG. 17 is a cross-sectional illustration depicting a die casting step according to Embodiment 2;

FIG. 18 is a cross-sectional illustration, taken along a line XVIII-XVIII of FIG. 17 depicting a first projecting portion, second projecting portion, and outlet cylindrical portion according to Embodiment 2; and

FIG. 19 is a cross-sectional view of an intermediate formed body according to Embodiment 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term “circumferential direction” refers to the rotational direction of the impeller and the term “axial direction” refers to the direction of the rotation axis of the impeller. The term “front” refers to the side on which the inlet port opens in the axial direction and the term “back” refers to the opposite side.

In the die casting step, the first projecting portion and the second projecting portion are preferably abutted against each other. In such a case, the volume of the residue portion in the intermediate formed body can be reduced and therefore the man-hours in the cutting and removal step can be reduced. As a result, it is possible to further improve the productivity for producing the compressor housing.

Furthermore, the intermediate formed body preferably has the residue portion only partly existing on the inner wall surface of the outlet cylindrical portion. In such a case, the area to be cut in the inner wall surface of the outlet cylindrical portion in the cutting and removal step can be reduced. As a result, it is possible to further improve the productivity for producing compressor housings.

Furthermore, preferably, the first projecting portion has a first projecting mold surface for forming a part of the inner wall surface of the outlet cylindrical portion in the intermediate formed body and the second projecting portion has a second projecting mold surface for forming another part of the inner wall surface of the outlet cylindrical portion in the intermediate formed body. In such a case, the parts of the inner wall surface of the outlet cylindrical portion can be formed efficiently by the back mold and the front mold. Thus, scroll pieces with enhanced design flexibility can be produced more easily with good productivity.

In the die casting step, it is preferred that the projection end of the first projecting portion is located closer to the front end than the projection end of the second projecting portion. In such a case, the volume of the residue portion in the intermediate formed body can be reduced and therefore the man-hours in the cutting and removal step can be reduced.

Embodiment 1

An embodiment of the method for producing a compressor housing for a turbocharger will be described with reference to FIGS. 1 to 16. As shown in FIG. 2, the compressor housing 1 is able to house an impeller 10.

As shown in FIGS. 1 to 5, the compressor housing 1 includes an inlet port 11, a scroll chamber 12, an outlet port 13, and an outlet communicating section 14. The inlet port 11 is formed adjacent to the front end of the impeller 10 and opens to the front end in an axial direction Z. The scroll chamber 12 is formed on an outer circumferential side of the impeller 10 in a circumferential direction. The outlet port 13 opens to the front end in an axial direction Z on an outer circumferential side of the inlet port 11. The outlet communicating section 14 communicates between the outlet port 13 and the scroll chamber 12.

The compressor housing 1 is constructed by assembling a scroll piece 2 and a shroud piece 3, which are each formed as a discrete part, together in the axial direction Z. The scroll piece 2 includes an inlet cylindrical portion 21, a front side wall section 22, and an outlet cylindrical portion 23. The inlet cylindrical portion 21 makes the inlet port 11 and has a through hole in the axial direction Z. The front side wall section 22 is located on an outer circumference side of the inlet cylindrical portion 21 and makes a front area of the wall surface of the scroll chamber 12. The outlet cylindrical portion 23 extends from a region in the circumferential direction of the front side wall section 22 and makes the outlet communicating section 14 and the outlet port 13.

As shown in FIG. 5, in the outlet cylindrical portion 23, the inner wall surface of the outlet communicating section 14 is curved so as to smoothly connect between the inner wall surface of the scroll chamber 12 and the inner wall surface of the outlet port 13. As shown in FIGS. 2 to 4, the shroud piece 3 includes: a shroud press-fit portion 31 in a cylindrical shape to be press-fitted into the inlet cylindrical portion 21; an inner circumferential wall section 32 making an inner circumferential area of the wall surface of the scroll chamber 12; a shroud surface 33 opposed to the impeller 10; and a diffuser surface 34 extending from the shroud surface 33 to the scroll chamber 12.

For fabrication of the scroll piece 2, a die casting step and a cutting and removal step are performed. As shown in FIGS. 7 to 12, in the die casting step, die casting is carried out using a back mold 4 and a front mold 5 to form an intermediate formed body 20.

As shown in FIGS. 7 and 10, the back mold 4 includes a first projecting portion 41 projecting toward the front side. The front mold 5 includes a second projecting portion 51 projecting toward the back side. The front mold 5 is a mold being movable back and forth relative to the back mold 4 in the axial direction Z. As shown in FIGS. 11 and 12, the intermediate formed body 20 obtained by the die casting step includes residue portions 201 including a metal material left within the outlet cylindrical portion 23. As shown in FIGS. 7 and 8, in the die casting step, both the first projecting portion 41 and the second projecting portion 51 are disposed within the outlet cylindrical portion 23. In FIG. 8, the cross sections of the molds outside the outlet cylindrical portion 23 are omitted.

In the cutting and removal step, the residue portions 201 in the intermediate formed body 20 shown in FIGS. 11 and 12 are removed by cutting. As a result, the scroll piece 2 as shown in FIGS. 13 and 14 is obtained.

As shown in FIGS. 7, 9, and 10, the die casting forming molds used in the die casting step are made up of the pair of back mold 4 and the front mold 5 as described above. The paired molds are movable back and forth relative to each other along the axial direction Z. In the die casting step, other molds than the back mold 4 and the front mold 5, such as a core or a slide mold, are not used.

As shown in FIGS. 7 and 9, the back mold 4 and the front mold 5 each include mold surfaces for forming portions of the scroll piece 2. As shown in FIGS. 7 and 8, the first projecting portion 41 of the back mold 4 has a first projecting mold surface 411 for forming a part of the inner wall surface of the outlet cylindrical portion 23 in the intermediate formed body 20. The second projecting portion 51 of the front mold 5 has a second projecting mold surface 511 for forming another part of the inner wall surface of the outlet cylindrical portion 23 in the intermediate formed body 20.

Furthermore, as shown in FIGS. 7 and 9, the back mold 4 includes, in addition to the first projecting mold surface 411, mold surfaces for forming: an inner wall surface of the front side wall section 22 in the scroll piece 2; an area of the outer wall surface of the outlet cylindrical portion 23; a back area of the inner wall surface of the inlet cylindrical portion 21; and others. The front mold 5 includes, in addition to the second projecting mold surface 511, mold surfaces for forming: an outer wall surface of the front side wall section 22 in the scroll piece 2; an area of the outer wall surface of the outlet cylindrical portion 23; a front area of the inner wall surface of the inlet cylindrical portion 21; and others.

To form the intermediate formed body 20 in the die casting step, firstly the back mold 4 and the front mold 5 are mated to each other. In this state, the first projecting portion 41 and the second projecting portion 51 are abutted against each other as shown in FIGS. 7 and 8. A projection end 414 of the first projecting portion 41 is located closer to the front side of the intermediate formed body 20 than a projection end 514 of the second projecting portion 51. That is, the first projecting portion 41 and the second projecting portion 51 overlap each other in the axial direction Z. An end surface 412 formed at the projection end 414 of the first projecting portion 41 and a stepped surface 512 of the second projecting portion 51 are brought into surface-to-surface contact with each other in the axial direction Z. A side surface 413 of the first projecting portion 41 and a side surface 513 of the second projecting portion 51 are brought into surface-to-surface contact with each other in a direction approximately perpendicular to the axial direction Z.

Then, molten metal such as molten aluminum is injected into the cavity formed between the back mold 4 and the front mold 5. Then, the metal material within the cavity is solidified. At this stage, the intermediate formed body 20 of the scroll piece 2 is obtained within the cavity as shown in FIGS. 7 and 9. In this state, both the first projecting portion 41 and the second projecting portion 51 are disposed within the outlet cylindrical portion 23 of the intermediate formed body 20.

Then, as shown in FIG. 10, the back mold 4 and the front mold 5 are separated from each other relatively in the axial direction Z to accomplish coring-out. In this manner, the intermediate formed body 20, which is a body formed from a metal material, is obtained. As shown in FIGS. 11 and 12, the intermediate formed body 20 has a shape that is approximately the same as the shape of the scroll piece 2 to be eventually obtained (see FIGS. 13 and 14). However, the residue portions 201 remain within the outlet cylindrical portion 23 in the intermediate formed body 20. This is because, within the outlet cylindrical portion 23 of the scroll piece 2, there are portions that cannot be formed by the coring-out in the axial direction Z.

That is, within the internal space of the outlet cylindrical portion 23 to be obtained, there are space regions in which neither the first projecting portion 41 nor the second projecting portion 51, which are movable back and forth along the axial direction Z, can be disposed. The portions corresponding to the space regions become the residue portions 201 and remain in parts of the intermediate formed body 20. However, as shown in FIGS. 7 and 8, by disposing the first projecting portion 41 and the second projecting portion 51 within the outlet cylindrical portion 23 in such a manner that they each constitute a sufficiently large volume fraction, the volume of the residue portions 201 can be reduced. In the present embodiment, the residue portions 201 are present only partly existing at two locations on the inner wall of the outlet cylindrical portion 23, as shown in FIG. 12.

The residue portions 201 are removed by cutting in the cutting and removal step. In this manner, the scroll piece 2 having the desired outlet cylindrical portion 23 is obtained as shown in FIGS. 13 and 14. In the cutting and removal step, the residue portions 201 are cut and removed using a cutting tool such as a ball end mill, for example. Specifically, the residue portions 201 are cut and removed with a cutting tool being inserted into the outlet cylindrical portion 23 from the back side or front side of the intermediate formed body 20 or from both the back side and front side of the intermediate formed body 20. In this manner, the inner wall surface of the outlet cylindrical portion 23 is processed. For this process, numerical control cutting (i.e., NC cutting) using a multi-axis machine tool may be employed to increase the productivity.

In the manner described above, the scroll piece 2 can be obtained. An insert hole or the like for inserting a screw for securing the scroll piece 2 to a seal plate 6 can be formed as necessary by drilling or other means. As shown in FIG. 16, the compressor housing 1 is formed by assembling the shroud piece 3 to the scroll piece 2 in the axial direction Z. Specifically, the shroud press-fit portion 31 of the shroud piece 3 is press-fitted into the inlet cylindrical portion 21 of the scroll piece 2. The inner circumferential wall section 32 of the shroud piece 3 is smoothly connected to the front side wall section 22 of the scroll piece 2 to form the scroll chamber 12.

The shroud piece 3 can also be cast by die casting a metal such as aluminum. The shroud piece 3 is shaped such that coring-out in the axial direction Z is possible and therefore does not require a step corresponding to the above-described cutting and removal step.

Further, as shown in FIGS. 1 to 6, the seal plate 6 is assembled to the scroll piece 2, to which the shroud piece 3 has been assembled. As shown in FIG. 6, the seal plate 6 is an approximately disc-shaped plate. A flat diffuser opposite surface 61 is formed in an annular shape at the front surface of the seal plate 6. Also, an outer circumferential rising portion 62 projecting toward the front side is formed along approximately entire outer circumference of the seal plate 6. As shown in FIGS. 3 and 4, an outer circumferential concave surface 63 having a smooth concave shape, as viewed in the cross section containing the central axis of the compressor housing 1, is formed at the inner circumferential surface of the outer circumferential rising portion 62. As shown in FIGS. 3, 4, and 6, the outer circumferential rising portion 62 is shaped such that the height of the projection gradually changes along the circumferential direction. Further, as shown in FIGS. 5 and 6, in a region of the outer circumferential rising portion 62 in the circumferential direction, an outlet concave surface 64 is formed such that it smoothly connects to the outlet cylindrical portion 23 of the scroll piece 2.

When the seal plate 6 is assembled to the scroll piece 2, to which the shroud piece 3 has been assembled, the diffuser opposite surface 61 faces the diffuser surface 34 of the shroud piece 3. A diffuser passage 15 is formed between the diffuser surface 34 and the diffuser opposite surface 61.

When the seal plate 6 is assembled to the compressor housing 1, the compressor housing 1 is placed in a state in which the impeller 10 is disposed therewithin. In reality, as shown in FIG. 2, the compressor housing 1 is secured to the seal plate 6 assembled to the center housing of the turbocharger (not shown), in such a manner that the impeller 10 is disposed inside of the compressor housing 1. In the present embodiment the seal plate 6 is a discrete component separate from the center housing. However, the seal plate may be integral with the center housing as a part thereof.

Thus, as shown in FIGS. 3 and 4, in the state in which the compressor housing 1 and the seal plate 6 have been assembled together, the inner circumferential wall section 32 of the shroud piece 3, the front side wall section 22 of the scroll piece 2, and the outer circumferential concave surface 63 of the seal plate 6 are smoothly connected together. The scroll chamber 12 is completed within them. In the state of the compressor housing 1 before the seal plate 6 is assembled thereto, the space formed by the inner circumferential wall section 32 and the front side wall section 22 is also referred to as the scroll chamber 12. Further, as shown in FIG. 5, the outlet concave surface 64 of the seal plate 6 smoothly connects to the inner wall surface of the outlet cylindrical portion 23 of the scroll piece 2.

Thus, in the turbocharger, the compressor housing 1 is in a state in which the seal plate 6 has been assembled thereto as shown in FIGS. 1 to 5. The compressor housing 1 in this state houses the impeller 10 as shown in FIG. 2 to form the compressor.

The compressor takes in air through the inlet port 11 by means of rotation of the impeller 10. The intake air is delivered to the scroll chamber 12 from the impeller 10 through the diffuser passage 15. During this process, the intake air is compressed and the compressed air is delivered to the internal-combustion engine through the outlet port 13.

Now the functions and advantages of the present embodiment will be described. The above-described method for producing a compressor housing includes the die casting step and the cutting and removal step. In the die casting step, die casting is performed using the back mold 4 and the front mold 5, which are movable back and forth relative to each other in the axial direction Z. Further, the die casting is performed in such a manner that the first projecting portion 41 of the back mold 4 and the second projecting portion 51 of the front mold 5 are positioned within the outlet cylindrical portion 23. This makes it possible to easily form, by die casting, the intermediate formed body 20 having a shape close to the final shape of the scroll piece 2 without using a core or the like.

Then, the residue portions 201 in the intermediate formed body 20 are removed by cutting in the cutting and removal step, and thereby the scroll piece 2 can be readily produced. By performing the simple die casting step and the simple cutting and removal step in this manner, it is possible to readily produce the scroll piece 2. Consequently, production of the compressor housing 1 can be readily accomplished and therefore the production man-hours and the production cost can be minimized.

Furthermore, in the die casting step, the first projecting portion 41 and the second projecting portion 51 are abutted against each other. This makes it possible to reduce the volume of the residue portions 201 in the intermediate formed body 20 and therefore to reduce the man-hours in the cutting and removal step. Furthermore, the intermediate formed body 20 has the residue portions 201 only partly existing on the inner wall surface of the outlet cylindrical portion 23. Therefore, the area to be cut in the inner wall surface of the outlet cylindrical portion 23 in the cutting and removal step can be reduced. Consequently, it is possible to further improve the productivity for producing the compressor housing 1.

Furthermore, the first projecting portion 41 of the back mold 4 has the first projecting mold surface 411 and the second projecting portion 51 of the front mold 5 has the second projecting mold surface 511. This makes it possible to efficiently form the part of the inner wall surface of the outlet cylindrical portion 23 using the back mold 4 and the front mold 5. Thus, the scroll piece 2 with enhanced design flexibility can be produced more easily with good productivity.

In the die casting step, the projection end 414 of the first projecting portion 41 is located closer to the front side of the intermediate formed body 20 than the projection end 514 of the second projecting portion 51. This also makes it possible to reduce the volume of the residue portions 201 in the intermediate formed body 20 and therefore to reduce the man-hours in the cutting and removal step.

As described in the foregoing, with the present embodiment, it is possible to provide a method for producing a readily producible compressor housing for a turbocharger.

Embodiment 2

As shown in FIGS. 17 to 19, the present embodiment is an embodiment in which the first projecting portion 41 and the second projecting portion 51 are not abutted against each other in the die casting step. Specifically, as shown in FIGS. 17 and 18, the configuration is such that, when the back mold 4 and the front mold 5 are mated together, the first projecting portion 41 and the second projecting portion 51 are not abutted against each other with a clearance C formed therebetween. In this configuration, the molten metal enters the clearance C as well.

As a result, as shown in FIG. 19, the outlet cylindrical portion 23 of the intermediate formed body 20 is shaped such that the inside spaces do not pass therethrough. Specifically, the solidified portion of the molten metal that has entered the clearance C between the first projecting portion 41 and the second projecting portion 51 becomes a residue portion 202 within the outlet cylindrical portion 23 of the intermediate formed body 20. The residue portion 202 partitions the space within the outlet cylindrical portion 23 into the outlet port 13-side region and the scroll chamber 12-side region. In the present embodiment, the residue portion 202 is in the form of a film. Together with the film-form residue portion 202, residue portions 201 similar to the residue portions formed in the intermediate formed body 20 of Embodiment 1 also remain. The residue portions 201 and the residue portion 202 are continuously formed. The thickness of the film-form residue portion 202 is preferably as small as possible. The shape of the residue portion 202 is not particularly limited.

In the cutting and removal step, the film-form residue portion 202 is removed together with the other residue portions 201. With this operation, the inside space of the outlet cylindrical portion 23 is passed therethrough and the inner wall surface of the outlet cylindrical portion 23 is formed into the desired shape. In this manner, the scroll piece 2 (see FIG. 14) is produced. The other configurations are similar to those of Embodiment 1. Among the reference characters used in this embodiment, the characters that are the same as those used in Embodiment 1 represent elements or the like similar to those in the previous embodiment unless otherwise specified.

In this embodiment, the first projecting portion 41 and the second projecting portion 51 are not abutted against each other and therefore the dimensional accuracies of the facing surfaces of the first projecting portion 41 and the second projecting portion 51 need not be particularly high. As a result, it is possible to reduce the production cost. This embodiment has functions and advantages similar to those of Embodiment 1.

The present invention is not limited to the embodiments described above and various embodiments may be employed without departing from the spirit and scope of the invention. 

1. A method for producing a compressor housing for a turbocharger, the compressor housing being able to house an impeller, the compressor housing including an inlet port formed adjacent to a front side of the impeller, the inlet port opening to the front side in an axial direction; a scroll chamber formed on an outer circumferential side of the impeller in a circumferential direction; an outlet port on an outer circumferential side of the inlet port, the outlet port opening to the front side in the axial direction; and an outlet communicating section communicating between the outlet port and the scroll chamber, the compressor housing being constructed by assembling a scroll piece and a shroud piece, each formed as a discrete part, together in the axial direction, the scroll piece comprising: an inlet cylindrical portion making the inlet port and having a through hole in the axial direction; a front side wall section on an outer circumferential side of the inlet cylindrical portion, the front side wall section making a front area of a wall surface of the scroll chamber; and an outlet cylindrical portion extending from a region in a circumferential direction of the front side wall section, the outlet cylindrical portion making the outlet communicating section and the outlet port, the outlet cylindrical portion being configured such that an inner wall surface of the outlet communicating section is curved so as to smoothly connect between an inner wall surface of the scroll chamber and an inner wall surface of the outlet port, the shroud piece including a shroud press-fit portion in a cylindrical shape to be press-fitted into the inlet cylindrical portion; an inner circumferential wall section making an inner circumferential area of the wall surface of the scroll chamber; a shroud surface opposed to the impeller; and a diffuser surface extending from the shroud surface toward the scroll chamber, the method comprising: a die casting step of forming an intermediate formed body by die casting, the intermediate formed body having a residue portion including a metal material left within the outlet cylindrical portion, the die casting using a back mold having a first projecting portion projecting toward the front side and a front mold having a second projecting portion projecting toward a back side, the front mold being movable back and forth relative to the back mold in the axial direction; and a cutting and removal step of removing the residue portion in the intermediate formed body by cutting so as to obtain the scroll piece, wherein, in the die casting step, both the first projecting portion and the second projecting portion are disposed within the outlet cylindrical portion.
 2. The method according to claim 1 for producing the compressor housing, wherein the intermediate formed body has the residue portion only partly existing on an inner wall surface of the outlet cylindrical portion.
 3. The method according to claim 2 for producing the compressor housing, wherein the first projecting portion has a first projecting mold surface for forming a part of the inner wall surface of the outlet cylindrical portion in the intermediate formed body and the second projecting portion has a second projecting mold surface for forming another part of the inner wall surface of the outlet cylindrical portion in the intermediate formed body.
 4. The method according to claim 1 for producing the compressor housing, wherein, in the die casting step, a projection end of the first projecting portion is located closer to the front side of the intermediate formed body than a projection end of the second projecting portion.
 5. The method according to claim 1 for producing the compressor housing, wherein, in the die casting step, the first projecting portion and the second projecting portion are abutted against each other. 